Nuclear reactor fuel element with attached thermocouple



May 5, 1954 B. TURovLlN 3,132,077

NUCLEAR REACTOR FUEL ELEMENT WITH ATTACHED THERMOCOUPLE Filed Aug. 17, 1959 I operating temperatures.

of the invention will be understood by reference to the invention.

313,207? f NUCLEAR REACTR FUEL ELEMENT WITH l ATTACHED THERMocoUPLE 1 Bernard'lurovlin, San Diego, Calif., assignor toGeneral Dynamics Corporation, New York, N.Y., a corporation Ang. 17, 1959, Ser. No. 834,124

`; Filed f 4 Claims. (Cl. 176-68) element construction which provides means for determinz ing, under loperating conditions, the temperature at various selected pointswithin the fuel element.

The principal object of the invention is the provision of a f uel element incorporating means alfording measurement ofthe temperature at selected points in the fuel element'containing the issionable material. A further objectof the invention is the provisionlof such fuel element having characteristics which are not significantly diierentffrom al similar fuel element which does not include means for determining the temperature at selected points within the fuel element. Still another object of the present invention is the provision of a fuel element incorporating temperature indicating means whichv is simple in construction and effective over a wide range of Other objects and advantages following description and tothe accompanying drawings in Which: f

.FIGURE 1 is a perspective view,ipartially broken away,

. of 'afuel element embodying various features of the in- ,Ve'ntiom` FIGURE 2 is an enlarged sectional view of a portion of -th'e fuel element shown in FIGURE 1, illustrating I the arrangement for locating a thermocouple within the fuel element;

FIGURE 3 is' an enlarged sectional View of that portion of thefuel element construction which includes the coupling shown at the top of FIGURE 1; and

FIGURE 4 is an enlarged View, partially in section, cfg-one of the connectors shown in FIGURE 3 and the parts attached thereto. Asshown'in the drawings, a

fuel element in accord- V ance/with the invention includes a sealed can or containe 11 in which is located a fuel body 13 of an alloy Y containing -ssionable material.

Situated within the fuel body-13 are a series of vertically spaced tapered recesses V1'5 which extend inwardly of the fuel body to spaced points adjacent the center line thereof and, in one in- United States Patent ice The fuel Vbody 1s is located entrauy within the can! 11 and takes the form of an'elongated cylinder having an outer diameter corresponding with the inner diameter of the can. While various fissionable alloys can be used, one fuel body which has been utilized consisted of a solid, homogeneous, hydrided zirconium uranium' allOy (e.g. approximately: 9l% zirconium, 8% uranium, 1% hydrogen). The fuel element illustrated in the drawings, which fuel element is of the general form utilized in Va specic reactor manufactured by the assignee of this invention, includes on each side of the fuel body 13 a cylinder of graphite 25 and 27. This graphite functionsy both as a moderator and as a neutron'reiiector. 1

As mentioned previously, the fuel body 1 3 is provided with a series of recesses 15, all of which are generally identical and into which the thermocouple carrying inserts 17 are received for measuring the temperature within the fuel body at selected points. The' recesses are each inwardly tapered to provide, in cooperation with the tapered inserts, a friction fit incident. to driving the insert into the fuel body recesses. This provision providesv for positive anchoring ofA the inserts, thereby positively locating the thermocouples 19 carried by the inserts 17.`V In addition, this provision results in an intimate contact bel.l

tween the inserts and the fuel body having good heat transfer characteristics. i'

Three of the recesses extend radially along a downward incline of about degrees'from points spaced along the length and around the ycircumference of the fuel body. The inner ends of the recesses are respectively located at points spaced along the center line 20 of the fuel body. The other recess extends horizontally across the fuel body from a point between the upper two inclined recesses 15 to a point just within the. outer surface of the fuel` body. Thus, the thermocouple located at this point l measures the temperature at the skin or outer surface lof tion, being formed of ssionable alloy, and having a tapered outer surface corresponding to the shape of the recesses. In the preferred embodiment, the inserts 17 are of a zirconium uranium alloy which has substantially the same composition as the fissionable alloy irithe fuel body with the exception that the alloy has -not-been hydrided. The use of this material avoids temperature perturbations which might otherwise occur if inserts were used of materials having thermal and/or iissioncharacteristics different from those of the fuelbody.

stance, extends horizontally across the -fuel body to a location adjacent the outer surface or skin of the fuel body. .In reach of the recesses 15 there is received a tapered insert 17 of a iissionable alloy which carries a thermocouple 19 at its inner end. Each of the thermocouples 19 comprises a pair of wires 21 of dissimilar metal which are joined together and produce a measurable thermal E.M.F.'proportional to the temperature at the juncture of the wires. Each of the wires 2 1 extends out of the container 11for connectionwith asuitable measuring device (not shown) which is calibrated to indi-v vcate the generated by the thermocouple.

A The'can 11 in which the fuel body 13 is containedis fabricated from aluminum in the form of an elongated ycylinder having welded at one end, which shall be referred to asthe bottom, a bottom plug 23 which seals the bottom of the can and provides means for locating the fuelfelement in a suitable support or grid. Of course, the can 11 may be constructed with other shapes and from other materials and still obtain-the advantagesY of this I i 31 (see FIGURE 2) which includes an opening 33 'atthe inner end of the insert which is of smaller cross sec# AsV noted previously, each of theV inserts '17 carriesV at its inner end a thermocouple 19 which, as shown in FIGURE 2, is exposed to the lissionable material in the fuel body 13. In order to receive the thermocouple, each of the inserts is provided with a central passageway couple wires is stabilized and thewires are fxedly secured in the opening 33 by.welding them to the inner tip 'of the insert.

As the temperature within the fuel element may reach,

under operating conditions, a temperature of between 600 C. and 800 C. the metals chosen for the thermo# couples must be physically unaffected by these temperatures.

produce a detachable change in which is pro- `I atented May 5., 1964 In addition, the metals selected should not `ap` v preciably effect the reactivity of the Afuel body and mustV range and which'can be reproduced for calibration in accordance with the sensitivity desired. These requirements have been satisfied ir` the disclosed embodiment through thel use of 28 gauge Chromel, and Alumel Wires having glass braid insulation. Chromel is a trade- The wires extend from the inner tip of the inserts 17 to the upper end of the fuel body 13 through passageways Y31 in the inserts and throughV connecting grooves 35 which extend longitudinally along the outer surface of the fuel body. Above the fuel bodyr13 the wires 21 travel through a series of inclined holes or passageways 39 in the graphite cylinder 25 and merge into a single central vertical passageway 41 opening into the center of the top of the graphite cylinder.

The upper end of the container 11 is closed by an aluminum plug 43 which is suitably welded to the aluminum can or container in an inert atmosphere of argon gas. The plug 43 includes an upwardly extending hollow stem 4S, the outer Yend of which extends into one male component 47 of a compression type coupling 49. The plug 43 includes a central bore 51 which is aligned with the central passageway 41 in the graphite cylinder 25 and through which the thermocouple 'wires 21 extend. This bore is closed by a polyethylene wafer 52 and by an epoxy, as indicated at 53, to seal the container 11, thereby preventing escape of the ssionable products, and in addition, to stabilize theV thermocouple wires.

Connectable with the upper end ofthe fitting or coupling 49 is an aluminum tube 55 which extends to the exterior of the reactor. The aluminum tube S5, at its lower end, extends into the coupling 49 through a second .male component 57 which is similar to the component within the coupling 49 to insulated copper leads 61. InV

turn, the copper leads 61 extend through the aluminum tube to the exterior of the reactor and terminate in a connector suitable for connection with a device (not shown) for measuring the'EIMl-T. produced by the thermocouple so as to indicate'the temperature at the thermocouple junction.

The thermocouple Wires 21 are each electrically con- 'the longitudinal center line of said fuel body and a second y recess extending inwardly of said fissionable material to a' point adjacent the outer surface of said fuel body, an insert'of iissionable material in each of said recesses, said fissionable material in said inserts having similar heat transfer and nuclear characteristics as said issionable material in said fuel body, and a thermocouple carried at the inner end of each of said inserts with the junction of said thermocouple exposed to said ssionable matev rials in said insert and in said fuel body, each of said thermocouples being constituted by a pair of wires-which extend exteriorly of said container for connectiony to an indicating unit for measuring the temperature of said fuel body in the vicinity of said rst and second thermocouples. Y f

2. A fuel element for a nuclear reactor, said fuel element comprising a sealed container, a fuel body containl ing ssionable material located in said container, said fuel body having a recess therein, an insert containing Vissionable material received in and substantially filling nected to one of the copper leads 61 through individual tubular copper connectors 63 (see FIGURE 4). Each connector 63 includes a central bore 67v which is formed with one end larger than the other. In this connection, the thermocouple wire 21 is'silver soldered within the smaller end of the central bore, and the copper lead 61 is soft soldered within the bore at the large end. The entire electrical connecton is insulated by wrapping with a glass tape 69. Y

The described fuel element Vpermits accurate'measurement, 'under operating conditions, of temperatures up to 800 C. both at the skin and in the center of the ssionable alloy material. With the disclosed construction, temperature perturbations are avoided, and at the same time, the thermocouples are positively anchored. Moreover, the presence of the thermocouples has no significant' adverse effect on the reactivity of the fissionable material. Various features of the inventoin are set forth in the appended claims.

said recess, said fissionable material in said insert having similar heat transfer and nuclear characteristics as said lissionable material in said fuel body, a pair of Wires constituting a thermocouple carried by said insert at its inner end With the junction of said wires exposed to said issionable'materials in said insert and in said fuel body, said insert including a passageway leading from the exterior of said fuel body to said thermocouple, saidV wires extending through said passageway and exteriorly of said container for connection to an indicating unit for measuring the temperature of said fuel body in the vicinity of said thermocouple.

3. A fuel element 'for a nuclear reactor, said fuel element comprising an elongated cylindrical container, a cylindrical fuel body located in said container, said fuel body consisting Vof an alloy containing ssionable material and having an outer diameter corresponding to the inner diameter of said container, a plurality of inwardly tapered recesses extending radially inwardly of said fuel elementV and terminating in longitudinally spaced apart relation to one another adjacent the center line of said fuel body, an additionalA inwardly tapered recess extending inwardly of said fuel body to adjacent the outersurface of said fuel body at a point spaced from the entrance of said additional recess, a tapered insert received in and substantially filling each of said'recesses, said inserts consisting of an alloy of fissionable material having similar heat transfer and nuclear characteristics as said ssionable material in said fuel body, a thermocouple carried by each of said inserts atftheir inner ends with the junction of said thermocouple exposed to said ssionable materials in said inserts and in said fuel body, said thermocouples comprising a Chromel and an Alumel wire, avpassageway in each of said inserts leading from said groove along the outer surface of said fuel body leading from each of said passageways to one end of said fuel thermocouple to the outer surface' of said fuel body, a l

body, connecting means secured to said container at the end thereof corresponding with said one end of said fuel body, a barrier's/ealing said container at the end thereof K corresponding with said one end of said fuel body, hollow means detachably connected to said connecting means and extending to the exterior of the reactor, said thermocouple wires being covered with glass tape insulation, extending through said passageways, through said grooves, Vthrough said barrier, thereby stabilizing said wires in relation to one another and in relationto said container, and being connectable through said hollow meansl Y container, a fuel body containing fissionable material 1ocated in said container, said fuel body having a recess extending inwardly of said iissionable material to adjacent the center of said fuel body, an insert of fissionable material occupying said recess, said ssionable material in said insert 'having similar heat transfer and nuclear chari acteristics as said iissionable material in said fuel body,

a thermocouple carried by said insert at its inner end with the junction of said thermocouple exposed to the fissionable materials in said insert and in said fuel body, and means connected to said thermocouple and extending exteriorly of said container for connection to an indicating unit for determining the temperature in the vicinity of said thermocouple'.

References Cited in the le of this patent UNITED STATES PATENTS Kanne Oct. 14, 1958 Morris et a1 Sept. 19, 1961 Guneratne et al Aug. 28 1962 FOREIGN PATENTS Great Britain Feb. 19, 1958 Belgium `Mar. 31, 1958 Australia July 28, 1958 France Apr. r27, 1959 Great Britain Aug. 10, 1960 OTHER REFERENCES AEC Document IDO-16318, June 14, 1957, page 19. 

1. A FUEL ELEMENT FOR A NUCLEAR REACTOR, SAID FUEL ELEMENT COMPRISING A SEALED ELONGATED CONTAINER, AN ELONGATED FUEL BODY CONTAINING FISSIONABLE MATERIAL LOCATED IN SAID CONTAINER, SAID FUEL BODY HAVING A FIRST RECESS EXTENDING INWARDLY OF SAID FISSIONABLE MATERIAL TO ADJACENT THE LONGITUDINAL CENTER LINE OF SAID FUEL BODY AND A SECOND RECESS EXTENDING INWARDLY OF SAID FISSIONABLE MATERIAL TO A POINT ADJACENT THE OUTER SURFACE OF SAID FUEL BODY, AN INSERT OF FISSIONABLE MATERIAL IN EACH OF SAID RECESSES, SAID FISSIONABLE MATERIAL IN SAID INSERTS HAVING SIMILAR HEAT TRANSFER AND NUCLEAR CHARACTERISTICS AS SAID FISSIONABLE MATERIAL IN SAID FUEL BODY, AND A THERMOCOUPLE CARRIED AT THE INNER END OF EACH OF SAID INSERTS WITH THE JUNCTION OF SAID THERMOCOUPLE EXPOSED TO SAID FISSIONABLE MATERIALS IN SAID INSERT AND IN SAID FUEL BODY, EACH OF SAID THERMOCOUPLES BEING CONSTITUTED BY A PAIR OF WIRES WHICH EXTEND EXTERIORLY OF SAID CONTAINER FOR CONNECTION TO AN INDICATING UNIT FOR MEASURING THE TEMPERATURE OF SAID FUEL BODY IN THE VICINITY OF SAID FIRST AND SECOND THERMOCOUPLES. 